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Old 06-23-2004, 11:33 PM
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How to fix/prevent these bad paint results

I have done two paint jobs before but never got to totaly fixing it.The side panels of the vehicle look fairly even but on the top panels especially the roof I got a 'striped' effect from the overlapping. Both these were sprayed in open air (no booth) with no clear coat. Did I do something wrong here? Will clear fix it or is it normal and just needs to be color sanded and buffed? I do understand that even after clear it needs sanding and buffing. Within the next few months I'll be doing my 53 Chevy and would like to do it myself than farm it out.

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Old 06-23-2004, 11:45 PM
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Nothing will hide the strips except more color. They will not sand out, Paint applied with to much pressure and or to dry even a narrow pattern, will all cause stripes ( ghosting ).

If your going to clear coat it now, you need to use an aqrlic enamel or urethane clear, not the same clear that you would use with a BC CC system. If you get the clear on right you should not have to sand and buff it.

Troy
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Old 06-24-2004, 05:09 AM
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Thanks Troy

One thing I can say is that I don't have a pressure regulator before the spraygun. What sort of pressure should it be set to in any case? I'm not sure about if I spray a too narrow pattern. If it's too dry would it mean that I'm holding the gun too far from the work or have I not got enough thinners added or is a combination?
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Old 06-24-2004, 07:39 AM
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A regulator and gage is a must when painting.

40-45 lb at the gun.

should have about 12-14 inch pattern, And overlap 1/2 way on each pass.

I always use a slow thinner to get a better flow before it dries.

Always refer to the tech. sheet for what ever brand of paint your using for mixing directions.

Troy
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Old 06-24-2004, 09:19 AM
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Let's not say what pressure until we know what gun is being used. HVLP, Conventional, Brand? There are some BIG variables in pressures used depending on the gun.

You are not spraying too dry, that I guaratee you. It is the opposite, you are spraying too wet. Think about, it has happened on the top surfaces only, and mostly on the highest point, the roof. You can only hold the gun so far away from the roof standing next to the car, you just aren't getting it up high enough. OR you are not moving fast enough.

On any car that just about any painter paints, you are going to have more material on the top surfaces. It is human nature, most anyone will do it. You can take your time and "watch" it go on. There is no fear of runs, the gun gets heavy and you start "draging". These are all reasons why this happens.

You need to back off a little, and maybe even do a criss cross pattern.

In my early days painting I sprayed lacquers. I was lucky enough to work under a real master at autobody and paint doing high end restorations. One of the things he taught me stays with me today and really helps with issues such as this.

It's the concept of "moving the dry spot". With lacquer you were spraying eight or ten coats and lacquer drys real fast. So if you were to start and stop every pass on each panel at the same place there would be a VERY dry spot at that point. So he taught me to "move the dry spot around". For instance paint the front fender ending at the door, then paint the door ending at the fender and the quarter then start the quarter ending at the door and the rear bumper. NEXT COAT: Paint the front half of the fender ending at the wheel well, paint the rear half of the fender ending in the middle of the door, paint the back half of the door ending in the middle of the quarter, paint the rear of the quarter. NEXT COAT: move the dry spot somewhere else.

Now, I am not saying you need to do exactly this, but to just keep in mind the procedure and what is happening when you start and stop at the same place.

Let's move this to the roof where you are having trouble. You are likely starting each pass on the edge of the roof right? Right in the exact same place, each time, the edge of your pattern is ending right in the same place. I will put money on it, your roof has more paint thickness in stripes on the roof!!

This is very common, don't feel bad. Look at a paint job that has failed, cracking, peeling, etc. Many times it will fail in stripes on the upper horizontal panels because of this. And Roofs will almost always fail right down the middle first. That is where the most paint is applied by most painters.

With all that in mind, get the gun make and style to us so we can give you the exact pressure and try it again. Go out and do some "dry runs" with your gun to see what you ARE doing, and what you can do with the guns travel.

On the overlap of passes, you could go up to 75% sometimes. It really depends on how wet you are putting it on.

Below is an article I have writen on gun travel it may be of help.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

"Basics of Basics" Gun travel
By Brian Martin

The sequence of how you walk around a car painting is really “learned”. If you understand the “why” the “how” will come to you.

I started out painting lacquer completes on restorations in the late seventies. My boss preached a lot of tricks and they have proven to hold up over the years.

On a 15 coat lacquer job you definitely didn't want the dry spot in the same place with every coat, so you have to “move it around” he would say. This has always stuck in my head, move the dry spot around or "chase" it. I start at a different point every coat, so that dry spot is moved, every coat. As you enter and exit a panel, you must do this little "dance" with the dry spot.... Coaxing it along from one panel to the next.

Doing the roof first lets it stay wet while you go on. If you do the hood first and then the roof, the overspray from the roof falls on the hood and "dries" it. This is what happens with every panel; it is just on a smaller order.

As far as "carrying" the gun, this is a long learned skill. But the basis is the idea that you are a ROBOT and you are to hold the gun a certain distance from the surface of the panel. This distance MUST BE maintained. The height is the same way, as you go across the panel (commonly called "down" the panel even though you are not going "down" but across) the height MUST BE maintained. So your overlap % is maintained. These two things are what keep each coat uniform with an equal/even about of product being applied.

So with this in mind what ever YOU do to "make" the gun do this is up to you.
Some of us look like a Ballerina painting, others a mechanical robot.

All the time I spent boxing helps me a bunch. I stay on the balls of my feet with knees bent and carry the gun out in front of me. Everything that happens between the gun and the soles of my feet is a fluid motion. I watch the paint hitting the surface, and with my peripheral vision look ahead for where the gun has to go.

You need to separate the body and the gun and think about "where" the gun needs to be, your body will make it go there.

I remember watching a pinstriper (who was a childhood friends dad) stripe a very long front engine rail, he just walked backwards down the length of it with his hand flowing over the top of the rails in the same fashion I have talked about here. His Dagger brush left PERFECT stripes, it was amazing. Well holding a spray gun is no different. After a while you can walk down a 40' semi trailer and the pass you are spraying looks like that pinstripe!

Practice on a car with no paint, just move up and down (across) the panels holding the gun that perfect distance. If you waver, it isn't the end of the world, there are many factors to "makeup" for your "mistakes" but the closer you maintain the gun to perfection the better your work will be.
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Old 06-24-2004, 01:30 PM
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Thanks a hell of a lot for your time and effort for such a good explanation! That does clarify a lot for me and it makes perfect sense. As far as the spry gun is concerned, I can't remember the brand. It's a cheapish one though. It's is a low pressure gravity feed type.

Do I need to move the dry spot around like that with primers too or is it more relevant to colors and clears?
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Old 06-24-2004, 04:05 PM
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Handling the paint gun to get a good paint job is something that will take a while to learn, you don't pick it up over night. Practice, practice, and more practice.

Most painters use a painters bench, one on each side of the car.
I wont go into detail and confuse you, as there is not much room left after martins book, but it has some good pointers in it.

Quote-posted by martinsr, __________________________________________________
You are not spraying too dry, that I guarantee you. It is the opposite, you are spraying too wet. Think about, it has happened on the top surfaces only, and mostly on the highest point, the roof. You can only hold the gun so far away from the roof standing next to the car, you just aren't getting it up high enough. OR you are not moving fast enough
__________________________________________________ _

Moving the gun to fast will cause dry stripes.
And getting the gun to close to the surface will cause dry stripes
because the pattern is to narrow, and the pressure is to great.
All of this causes a dry edge between passes.
Not enough material being applied WELL CAUSE DRY EDGES.
Applying to wet or to much material will not cause dry edges,I GUARANTEE IT.

Troy
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Old 06-24-2004, 10:56 PM
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Troy, you are right, I was thinking about "tiger stripes" or metallic mottling, not dry spots. You are right also that it doesn't come overnight. However, with a little information the learning curve isn't quite so steep.

Neophyte, are we talking dry stripes or "mottling" of some sort like metallic or pigment mottling in these stripe patterns?


Troy is right, you would need some really separated passes to spray too wet and end up with dry stripes on the edges of the pass. If they are dry stripes, it is likely the opposite of what I was saying with the too slow, too wet passes.

That doesn't change a bit of what I was saying about the dry spots though.

Is it important with primer, sure, it is important with everything you spray. This is it in a nutshell, the perfect application of primer, sealer, paint, clear, anything, is a layer of product that is uniform over the whole item being painted.

Let me exaggerate think of it as a big decal. If you were to apply a big decal over the car (this has actually been studied by the paint manufactures back in the early days of VOC study) then the "paint" would be an exact mil thickness over the entire thing right?

Your goal with applying paint, primer, clear, what ever, is to make it as close to the decal analogy as you can. A perfect film thickness over the whole thing. When ever you start or stop a pass you are going to put a little more product right at that point. So if you apply coat after coat right in one spot, you will have more product there.

I am sure you have seen a candy paint job that has darker areas at the door seams, it was caused because the guy didn't follow this rule, to move the dry spot (or simply the breaking point of each group of passes).

One way to apply primer is refered to as the "reverse method". That is where you prime a spot out to the largest point with the first coat. You then apply the next coat within that one, then the next within the last and so on. What this does it keeps the outer edge thinner so it feathers out nice, and keeps the overspray (dry spot) within the primer and helps melt it away.

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Old 06-25-2004, 02:35 AM
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Quote:
Originally posted by MARTINSR
Troy, you are right, I was thinking about "tiger stripes" or metallic mottling, not dry spots. You are right also that it doesn't come overnight. However, with a little information the learning curve isn't quite so steep.

Neophyte, are we talking dry stripes or "mottling" of some sort like metallic or pigment mottling in these stripe patterns?
Too be honest I'm not too sure what's meant by "mottling". To me it looks like dry stripes i.e. widish shiny stripes and narrow dull stripes. With my second "spray job" the roof of the car basically had a noticable dull stripe running down the centre from when I sprayed the left halve from the left side and then the right halve from the right side. The hood especially had dull stripes along the length of each stroke. I didn't really notice anything strange from what I can remember at the end of the panels where the "strokes" stopped and started.

I am now just waiting for the car to come back from the sandblaster. I wanted it back by tomorrow but the guys have another big job which had to be finished by today so I unfortunately have to wait till next week. The guy has done a quite a few cars before so he knows what it takes not to warp the metal. He, for instance, doesn't try and blast off body filler as he reckons it's then too easy to warp/stretch the metal.

Now I just need to sit and read all the given instructions a few times over to get it imprinted in my head and then go out and practise. I've still got the Jaguar parts car and some paint so I'll let you know how it goes.
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Old 06-25-2004, 08:22 AM
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Troy was right all of the following text in my post does not apply.

You are not spraying too dry, that I guaratee you. It is the opposite, you are spraying too wet. Think about, it has happened on the top surfaces only, and mostly on the highest point, the roof. You can only hold the gun so far away from the roof standing next to the car, you just aren't getting it up high enough. OR you are not moving fast enough.

The rest of my advice will work for you.

I was wrong, I thought it was "mottling". Mottling is when you get metallic particles "grouping" together instead of laying out nice. It will happen a lot in stripes on the top surfaces for the reasons I discribed.

Your dry stripes are caused by the too narrow a pattern, too fast movement, too high shop temp, too fast solvent (for colder weather) not enough overlap.

I have to ask, when you say you painted this without a booth, you don't mean out side do you? If you were, THAT may be your biggest problem. If you are painting outside in the sun, WOW, that can mess you up big time. The surface of the car is VERY hot and the paint would flash off VERY FAST.
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Old 06-25-2004, 09:19 PM
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Quote:
Originally posted by MARTINSR
I have to ask, when you say you painted this without a booth, you don't mean out side do you? If you were, THAT may be your biggest problem. If you are painting outside in the sun, WOW, that can mess you up big time. The surface of the car is VERY hot and the paint would flash off VERY FAST.
Umm, yeah ... I think that was my one major problem apart from the inexperience. I did actually do it outside in the sun. It's actually quite obvious but it just never registered in my mind as a major factor. Well, now I'll definitely do something about it. Problem though is that my garage is only a single garage of about 5 - 6 metres by about 3.5 to 4 metres. Now, with all my tools and equipment there's not enough room left for parking a car let alone spray in it. I think it was in the knowledge base that I saw an article on making a make-shift booth using pvc tubing and plastic sheeting. Will this still make it too hot even with the ventilation and maybe a darkish, non-clear roof section? I assume I would still need a 'slow' thinner? Is that the correct term to ask for at the paint shop?
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Old 06-25-2004, 11:45 PM
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Man, all this and that is what it was! LOL, yes that heat will do exactly what you are talking about.

The "booth", it will be just as bad.

Is there a real booth in town you can rent?
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Old 06-26-2004, 12:17 AM
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First of all you have to have some way to regulate the air pressure to what ever the gun and paint manufacture recommends. You can't use the pressure straight from the compressor.

Adjust the pattern so it is even vertically, and about 12-14 inches, holding the gun about 16-18 inches from the surface.

Mix the paint strictly by the tech. sheets from the paint suppler.
The higher the temperature the slower the thinner needs to be, if it's really hot, use some retarder.

And remember to overlap each pass by at least 50%.
When painting the top, start at the edge, go to the center, then go around to the other side, start at the center and go out to the edge. That should take care of the dry streaks.

Hope this helps,Good Luck.

Troy
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Old 06-26-2004, 01:54 AM
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Thanks a lot, Martin and Troy! I'll go and see if there's any booth's open to the public for renting but I nearly doubt it as I havent seen any ads in the local motoring mags even though there are tons of panel beating shops. Even if the home/diy guy isn't so far and few in between, it's as if the industry doesn't support them. Everybody's excuse is that it not worthwile etc, etc. The same goes for when one need special/custom parts or work done. The attitude is one of "why do you want to do that" or "it's gonna be too expensive for what it's worth". Everybody doing laser cutting for instance has a minimum job charge which means you need to have quite a few thing you want cut. Including V.A.T. it's around ZAR320 so you pay that even if the normal cost of the part would have been ZAR50. As you know how it goes with building a car at home, you will just never finish if you need to work like that. So you end up doing things yourself.

But enough of that negativity. I'll go out anyway in search of a rentable booth. I'll let you guys know how it goes. You have made me much "wiser" with your advise.LOL.
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Old 06-26-2004, 08:37 AM
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Neophyte, they may not advertise it, go and ask. There are a few shops that rent their booths here in town, you wouldn't know that if you didn't go ask them.

I have to tell you, your garage is about as big as some booths. And it is about as big as a garage I had where I painted a number of cars. You just need to clear the thing out.


Just remember to protect yourself and your family from the fumes, they can be very dangerous.

Good luck!
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